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blood diseases

Anemias are classified on morphological grounds. Macrocytic anemia, in which the average size of circulating red cells is larger than normal, results from impaired production of red cells—e.g., when vitamin B
12 or folic acid is lacking. In other circumstances—for example, when there is a deficiency of iron—the circulating red cells are smaller than normal and poorly...

characteristics

Structurally, the anemias generally fall into the following types: (1)
macrocytic anemia, characterized by larger-than-normal red cells (e.g., pernicious anemia), (2) normocytic anemia, characterized by a decrease in the number of red cells, which are otherwise relatively normal (e.g., anemia caused by sudden blood loss, as in a bleeding peptic ulcer, most cases of hemophilia, and purpura), (3)...